Embossing has long been used as a method to treat base paper for sanitary paper products to make those paper products more absorbent, softer and bulkier than the unembossed paper. The prior art discloses three methods of embossing paper between a pair of patterned embossing rolls. In the first method, one embossing roll has only male projections and the other embossing roll has only female recesses. This type of male-female embossing rolls is disclosed in U.S. Pat. No. 4,339,088-Niedermeyer at column 2, lines 25-37. The Niedermeyer patent is also relevant to a preferred embodiment of this invention because of its disclosure that by employing a pattern repeat in the machine direction that is equal to or greater than the circumference of the finished roll of paper, nesting and breakdown of the embossments in the roll can be retarded. in a second embossing method, both embossing rolls have only male projections. Such male-to-male embossing rolls are disclosed in U.S. Pat. No. Re. 27,453-Schutte, et al. and U.S. Pat. No. 3,817,827-Benz, both patents being assigned to the assignee of this application. In a third embossing method, both rolls have male projections and female recesses. During embossing the male projections of one roll extend into mating female recesses of the other roll and the male projections of the other roll extend into mating female recesses of the one roll. This type of embossing is described in UK Patent Application GB No. 2132141A-Bauernfeind. In both rolls of Bauernfeind, a neutral plane completely surrounds each male projection and female recess. Bauernfeind also discloses at page 1, lines 86-90 that the embossing elements can have both regular and unsymmetrical shapes and that if the element has both a major axis and a minor axis, aligning the major axis in the cross-machine direction will result in less cross-machine direction tensile degradation than if the element is oriented with the major axis aligned in the machine direction.
It is an object of this invention to provide an improved method of forming bosses in sanitary paper product.
Another object of this invention is to provide an embossed paper that for a given base sheet paper, and at a given product cross-machine direction tensile level, has improved resistance to compressive force normal to the plane of the paper.
It is another object of this invention to provide an embossed sanitary paper product that better resists compressive forces when it is wound onto a core to form a rolled sanitary paper product.
And yet another object of this invention is to provide improved embossing rolls of the type in which both rolls have male projections, female recesses and a midplane.